Various devices and methods have heretofore been disclosed which relate to extruders for melting thermoplastic solid materials introduced into an input end, heated in a heated zone and then extruded through an output. A variety of these extruders exist including screw conveyers which are disposed for rotational movement within a barrel. Some of these screw conveyers include a first and second screw conveyer which are co-axially disposed in the barrel where one of said screw conveyers is disposed co-axially within the other screw conveyer.
For example U.S. Pat. No. 3,021,561 discloses two or more screws which run co-axially one within the other where the individual screw members are provided with screw helixes on the internal as well as external surfaces thereof.
Moreover U.S. Pat. No. 3,689,182 illustrates apparatus utilizing a screw type extruder for reducing a solid thermoplastic material to a fluid by maintaining a spiral body of continuous width of the material in a continuous contact with the barrel of the extruder and separating the melted fluid from the solid body by conducting it through radial passageways into a low pressure axially extending region of the extruded screw.
Moreover U.S. Pat. No. 3,924,842 discloses apparatus for preparing a plastic heated material from solids introduced into the apparatus, the apparatus including a barrel having a screw conveyer therein defining a channel for conveying the material downstream as the material is melted within the channel and a passage communicating with the channel at a downstream location and an upstream location, the locations being chosen such that the unmelted solids enter the passage at the downstream location and are carried through the passage in an upstream direction by passing the channel, to be reintroduced into the channel at the upstream location.
Moreover U.S. Pat. No. 4,290,702 relates to plasticating apparatus which operates continuously to plasticate material which is delivered intermittently to a molding device, the plasticating apparatus including a first screw conveyer which rotates in a barrel, a back feed passage within the first screw conveyer and a second screw conveyer in the back feed passage arranged to recirculate material in a circuit extending back through the back feed passage.
Yet another arrangement is shown in U.S. Pat. No. 4,387,997 which illustrates a plasticating extruder in which the screw conveyer includes an inner back feed passage communicating with the channel established by the main flight of the screw conveyer and a solids directing flight for directing unplasticated material into the back feed passage and segregating all ready-plasticated material from the unplasticated material in the channel.
A further arrangement is disclosed in U.S. Pat. No. 4,472,059 which illustrates multiple primary flights and corresponding multiple secondary flights defining multiple channels on the screw conveyer.
Finally U.S. Pat. No. 4,637,790 illustrates plasticating extruders including at least one inner screw conveyer within an outer screw conveyer in a barrel for receiving unmelted solid material from the channel of the outer screw conveyer and conveying the received unmelted solid material in the channel of the inner conveyer in a direction parallel to and axially co-extensive with the direction of travel of the material in the channel of the outer screw conveyer and melting the received unmelted solid material to bring melted material to a downstream location where the melted material from both channels merge to deliver a flow of fully melted material to a downstream discharge outlet. A vent may be located in the barrel in the vicinity where material enters the channel of the inner screw conveyer for improved venting as a result of the diversion of material away from the vent.
Other arrangements are shown on the web site at www.spar.com.
It is an object of this invention to provide an improved extruder for producing a thermoplastic material having a first and second portion.
It is another object of this invention to provide a method of producing an extruded thermoplastic material having a first and second portion.